I've found turning it off and on fixes it. Suspect some crufty app is eating the memory and it starts swapping. Still like the phone but the missus just got a nice Android one and I like the look of it (the f-off big "google search" works for me). The lock in and lack of Linux support are really beginning to get on my tits. Finally got cut and paste with the last upgrade.
Oh, and the Android phone came with *a cover* to protect it. Not brilliant but at least something. You have to buy one for your iPhone - probably the first thing most people do, in fact.
I must admit I couldn't go back to an "ordinary" phone now, but Andriod will have come a hell of a long way when my O2 contract is up ... already looks pretty good, and it supports google calendar out of the box.